Disc recording and/or reproducing apparatus having a disc cassette loading/discharging mechanism with a lock member responsive to a cassette insertion to unlock a sliding member

ABSTRACT

A magnetic disc recording and/or reproducing apparatus in which a magnetic disc cassette containing a magnetic disc provided with a center hub is loaded so that the center hub engages with a rotary shaft of a disc rotating motor to rotate the magnetic disc. A cam for displacing a magnetic head is fitted to the outer periphery of a boss supporting a bearing which supports rotatably the rotary shaft, so that the force from the cam can be transmitted to the magnetic head through a bearing utilizing the rotational movement having a high transmission efficiency. As a result, a pulse motor for displacing the magnetic head can be made compact in size and light in weight and the power consumption of the pulse motor can be reduced. The cam is interposed between the level of the magnetic head and the chassis and the rotary shaft of the disc rotating motor is used also as the rotation center for the cam via a bearing mechanism, so that the magnetic head can access any position. As a result, a positioning mechanism can be disposed in a small space, so that the magnetic disc recording and/or reproducing apparatus can be made compact in size and light in weight.

This application is a continuation of allowed application Ser. No.08/468,822, now abandoned, filed Jun. 6, 1995 which was Division ofabandoned application Ser. No. 08/271,576 filed Jul. 7, 1994, which wasa continuation of abandoned Ser. No. 07/686,393 filed Apr. 17, 1991,which was a division of abandoned application Ser. No. 07/550,852 filedJul. 10, 1990, which was division of Ser. 07/409,985 filed Sep. 19,1989,now U.S. Pat. No. 4,959,740, which was a continuation of abandonedapplication Ser. No. 07/328,734 filed Feb. 8, 1989, which was acontinuation of abandoned application Ser. No. 06/373,156 filed Apr. 29,1982.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a disc recording and/or reproducingapparatus and more particularly to a disc recording and/or reproducingapparatus in which a recording and/or reproducing head is moved radiallywith respect to a disc-like recording medium to record or reproduceinformation into or from the recording medium.

2. Description of the Prior Art

For example, a magnetic disc recording and/or reproducing apparatus issuch an apparatus that has a magnetic head to be moved radially relativeto a magnetic disc which is rotated so that information is magneticallyrecorded or reproduced along a track defined on the magnetic disc.

In such an apparatus of the type described above, the accuracy of thedisplacement of a magnetic head; that is, the accuracy of positioning amagnetic head at a desired position on the disc is dependent upon theaccuracy of a pulse motor as a driver for shifting the magnetic head andthe machining tolerances of various parts of the apparatus. In thisregard, the accuracies of such pulse motor and various parts arestrictly controlled.

Even if high precision parts are used, there arises a problem ofaccuracy of assembling these parts. If assembly tolerances vary, it isof no use to use high precision parts. In addition, a high assemblingaccuracy leads to an increase of manufacturing cost.

As a mechanism for displacing a magnetic head with respect to a magneticdisc, there is known a mechanism in which a head mount having a magnetichead mounted thereon is displaced through a cam by a pulse motor.However, unless the guide mechanism of the head mount is compact in sizeand light in weight, a large force is exerted on the cams and the pulsemotor. As a result, the output of the pulse motor must be increased andthe mechanical strength of the cam mechanism must be strengthened. Thismeans that the pulse motor and the cam mechanism become complicated inconstruction, large in size and heavy in weight, resulting in a highmanufacturing cost.

In addition, the magnetic head must be accurately positioned at adesired track. Especially, the same magnetic disc is used by variousmagnetic disc recording and/or reproducing apparatuses and compatibilityamong magnetic discs is required. Therefore, the magnetic head must beaccurately mounted on the head mount.

From this viewpoint, it is desired that the tolerance of the head mountwith which the magnetic head is mounted on the head mount as well as thedeviation of the position of a head chip relative to the head mount mustbe correctly adjusted.

Furthermore, there is a positioning mechanism of the magnetic head inwhich a cam is arranged around a rotating axis of the magnetic disc sothat the cam serves to position the magnetic head at a desired track onthe magnetic disc. In general, the base of the magnetic disc is made ofsynthetic resin, while the cam is usually made of a metal material.Accordingly, the expansion coefficients of both materials are differentfrom each other.

When the coefficient of linear expansion of the magnetic disc isdifferent from that of the cam for displacing the magnetic head, theposition of the magnetic head is deviated from a desired track dependingupon temperature. As a result, the reproduction output from the magnetichead is lowered.

If the reproduction output is lowered, it follows that correctinformation is not reproduced and there is the possibility thaterroneous information is likely to be reproduced so that the reliabilityof the apparatus is decreased.

Furthermore, it is usual that the pitch of a track to be formed on amagnetic disc is small, and accordingly it is necessary that the trackposition and especially the outermost track position are detectedcorrectly. Therefore, a highly accurate detection means is required inorder to detect the track position. This means that the apparatusbecomes very expensive.

SUMMARY OF THE INVENTION

The present invention was made to overcome the above and other problemsencountered in the conventional disc recording and/or reproducingapparatus and has for its object to provide a disc recording and/orreproducing apparatus which is extremely simple in construction and yetcapable of positioning a magnetic head at a desired position with ahigher degree of accuracy without being adversely affected by assemblytolerances.

In order to achieve the above object, in a first aspect of the presentinvention, a disc recording and/or reproducing apparatus comprises:

a recording and/or reproducing head for recording and/or reproducinginformation on and/or from a disc-shaped recording medium;

a rotary shaft for rotating the disc-shaped recording medium;

a hollow member which surrounds the rotary shaft without preventing therotation thereof;

a head positioning member having a cam which is rotatable around theouter periphery of the hollow member whose position relative to thecenter of rotation varies, and which positions the recording and/orreproducing head on the disc-shaped recording medium;

a head mount having an engaging portion for engaging with the camsurface and a mounting portion on which the recording and/or reproducinghead is mounted, and for displacing the recording and/or reproducinghead with respect to the disc-shaped recording medium in response to therotation of the cam; and

a biasing member for forcing the head mount against the hollow member sothat the outer periphery of the hollow member is made into contact withthe inner periphery of the head positioning member at a position in thedirection in which the head mount is forced to move.

Here, the hollow member may be a boss having bearings for rotatablysupporting the rotary shaft and the boss can be securely fixed to achassis. The inner periphery of the head positioning member may have aninner diameter larger than the outer diameter of the outer periphery ofthe hollow member. The rotation of the head positioning member may betransmitted from a drive means via a gear member. The center of therotation cannot be fixed by the force of the biasing member. The cam inthe head positioning member can be provided with a plurality of camsurfaces which are formed discontinuously, so that the position of therecording and/or reproducing head is varied stepwise in response to therotation.

It is a second object of the present invention to provide a discrecording and/or reproducing apparatus provided with a mechanism fordisplacing a head which is compact in size and light in weight so thatthe head can be correctly displaced from one position to another.

In order to achieve the above object, in a second aspect of the presentinvention, a disc recording and/or reproducing apparatus comprises:

a recording and/or reproducing head for recording and/or reproducinginformation on and/or from a disc-shaped recording medium;

a head mount on which the recording and/or reproducing head is mounted;

a first guide member extending in the radial direction of thedisc-shaped recording medium;

a head positioning member for displacing the head mount along the firstguide member to position the recording and/or reproducing head on thedisc-shaped recording medium; and

a bearing member disposed on the head mount for reducing a slidingfriction to be produced when the head mount is displaced along the firstguide member.

Here, the head mount may be provided with a second guide member disposedin parallel with the first guide member and a roller member for makingrolling contact with the second guide member. The bearing member maycomprise a roller bearing, or a sliding bearing made of a wear resistantmaterial such as ruby.

It is a third object of the present invention to provide a discrecording and/or reproducing apparatus provided with a positionadjustment mechanism capable of adjusting correctly the position of amagnetic head relative to a magnetic disc.

In order to achieve the above object, in a third aspect of the presentinvention, a disc recording and/or reproducing apparatus comprises:

a recording and/or reproducing head for recording and/or reproducinginformation on and/or from a disc-shaped recording medium;

a head mount on which the recording and/or reproducing head is mounted;

a head adjusting member disposed on the head mount for adjusting theposition of the recording and/or reproducing head on the head mount;

a pressing member for pressing the disc-shaped recording medium againstthe recording and/or reproducing head; and

a position adjusting member for adjusting the position of the pressingmember in the pressing direction of the pressing member.

Here, the pressing member and the position adjusting member may bedisposed on an arm having one end supported by the head mount and biasedto rotate toward the recording and/or reproducing head. The headadjusting member may have a first adjusting member for adjusting aposition of the head in the radial direction of the disc-shapedrecording medium and a second adjusting member for adjusting a positionof the head in the tangential direction of the disc-shaped recordingmedium.

It is a fourth object of the present invention to provide a discrecording and/or reproducing apparatus capable of preventing thedeviation between a track and a magnetic head.

In order to achieve the above object, in a fourth aspect of the presentinvention, a disc recording and/or reproducing apparatus comprises:

a recording and/or reproducing head for recording and/or reproducinginformation on and/or from a disc-shaped recording medium;

a head mount on which the recording and/or reproducing head is mounted;and

a head positioning member having a cam engaged with the head mount, sothat in response to the displacement of the cam surface, the head mountis displaced so as to position the recording and/or reproducing head onthe disc-shaped recording medium, the head positioning member being madeof a material having a coefficient of thermal expansion similar to thatof the base of the disc-shaped recording medium.

Here, the cam can rotatably surround a member which surrounds a rotaryshaft for rotating the disc-shaped recording medium without preventingthe rotation thereof. The head positioning member can be made of asynthetic resin material.

It is a fifth object of the present invention to provide a discrecording and/or reproducing apparatus capable of detecting correctlythe outermost track position with a simple mechanism.

In order to achieve the above object, in a fifth aspect of the presentinvention, a disc recording and/or reproducing apparatus comprises:

a recording and/or reproducing head for recording and/or reproducinginformation on and/or from a disc-shaped recording medium;

a head mount on which the recording and/or reproducing head is mounted;

a head positioning member which has a cam engaged with the head mount,so that in response to the displacement of the cam, the head mount isdisplaced so as to position the recording and/or reproducing head on thedisc-shaped recording medium;

an indicating member disposed to correspond to a predetermined camsurface of the cam for positioning the recording and/or reproducing headto the outermost position on the disc-shaped recording medium;

detection means for detecting the indicating member; and

control means responsive to the detecting means for confirming that therecording and/or reproducing head is positioned to the outermostposition on the disc-shaped recording medium and for controlling thedrive of the head positioning member on the basis of the detectedposition of the recording and/or reproducing head on the disc-shapedrecording medium.

Here, the cam can rotatably surround a member which surrounds a rotaryshaft for rotating the disc-shaped recording medium without preventingthe rotation thereof.

The detection means may have a movable member in the form of a leverhaving a first portion engageable with the indicating member and asecond portion whose displacement is detected by the detection means;and the distance between the pivotal point of the lever and the firstportion can be shorter than the distance between the pivotal point ofthe lever and the second portion, so that the displacement of the secondportion due to the engagement of the first portion with the indicatingmember is amplified in the second portion.

The detection means may have a non-contact sensor which is out ofcontact with the second portion of the lever. The sensor may be a lightsensor comprising a light emitting element and a light receivingelement. The light sensor may be a reflection type sensor which has alight emitting element and a light receiving element, both of which aredisposed on one surface of the second portion of the lever.Alternatively, the light sensor may be a light-transmission type sensorwhich has a light emitting element and a light receiving element whichare disposed on opposite sides of the second portion of the lever.

In a sixth aspect of the present invention, a magnetic disc recordingand/or reproducing apparatus comprises:

a magnetic head for recording and/or reproducing information on and/orfrom a disc-shaped magnetic recording medium;

a head positioning member having a cam which is rotatable around ahollow member which surrounds a rotary shaft for rotating thedisc-shaped magnetic recording medium without preventing the rotation ofthe rotary shaft, the cam being made of a material having a coefficientof thermal expansion substantially similar to that of the base of thedisc-shaped magnetic recording medium, and the head positioning memberbeing displaced by the rotation of the cam to position the magnetic headwith respect to the disc-shaped magnetic recording medium;

a head mount having a portion in engagement with the cam and a mountingportion for mounting the magnetic head;

a guide member extending in the radial direction of the disc-shapedmagnetic recording medium for guiding the head mount with a reducedsliding friction;

an adjusting member mounted on the head mount for adjusting the positionand/or condition of confrontation; i.e. contact or non-contact, of themagnetic head mounted on the head mount with respect to the disc-shapedmagnetic recording medium;

a biasing member for biasing the head mount toward the hollow member, sothat the outer periphery of the hollow member is made into contact withthe inner periphery of the head positioning member at a position in thedirection in which the head mount is forced to move;

detection means disposed to correspond to a predetermined cam surface ofthe cam in the head positioning member for detecting that the magnetichead is positioned to the outermost position on the disc-shaped magneticrecording medium; and

control means responsive to the output signal from the detection meansfor controlling the drive of the head positioning member.

The above and other objects, effects, features and advantages of thepresent invention will become more apparent from the followingdescription of preferred embodiments thereof taken in conjunction withthe accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an exploded perspective view showing a magnetic disc and ahead drive mechanism used to explain a first embodiment of aconstruction of a magnetic disc recording and/or reproducing apparatusfor a case in which the present invention is applied to such anapparatus;

FIG. 2 is a perspective view showing a chassis upon which the head drivemechanism is mounted;

FIG. 3 is a sectional view taken along line 3--3 in FIG. 2;

FIG. 4 is a sectional view taken along line 4--4 in FIG. 2;

FIG. 5A is a sectional view showing an embodiment of a construction ofone bearing of the head mount;

FIG. 5B is a sectional view showing another embodiment of a constructionof the bearing of the head mount;

FIG. 5C is a sectional view showing an embodiment of a construction ofthe other bearing of the head mount;

FIG. 5D is a sectional view taken along line 5D--5D in FIG. 5C;

FIG. 6 is a schematic view showing a construction of an outermost trackdetecting mechanism;

FIG. 7 is an explanatory view used to explain the operation of theoutermost track detecting mechanism;

FIGS. 8A and 8B are a sectional view and a fragmentary side view showinga track positioning mechanism, respectively;

FIG. 9 is an exploded perspective view showing one embodiment of acassette loading mechanism;

FIG. 10 is a perspective view showing the assembled cassette loadingmechanism;

FIG. 11 is a sectional view showing the cassette loading mechanismimmediately after the insertion of a cassette;

FIG. 12 is a sectional view showing the cassette loading mechanism intowhich a cassette is completely loaded;

FIGS. 13A-13G are schematic views used to explain the operation of aroller when loading the cassette;

FIG. 14 is a sectional view showing the cassette loading mechanismbefore the cassette is lowered;

FIG. 15 is a sectional view of the cassette loading mechanism after thecassette has been lowered;

FIG. 16 is a perspective view showing the relationship between thecassette loading mechanism and the chassis;

FIG. 17 is a perspective view showing the chassis upon which thecassette loading mechanism is mounted;

FIG. 18 is an explanatory view used to explain the arrangement ofprinted circuit boards upon which a control circuit is mounted;

FIG. 19 is a side view showing the chassis upon which the printedcircuit boards are mounted;

FIG. 20A is a block diagram showing one embodiment of the controlcircuit;

FIG. 20B is a graph illustrating the relationship between the rotationalspeed of a magnetic disc and the reproduced output voltage;

FIG. 21A is a schematic view used to explain recording tracks on amagnetic disc;

FIG. 21B is a schematic view used to explain recording tracks on whichinformation is coarsely recorded;

FIG. 21C is a schematic view used to explain recording tracks on whichinformation is densely recorded;

FIG. 21D is a schematic view used to explain a recording system employedin the embodiment of the present invention;

FIGS. 22A-22C are graphs illustrating reproduced output characteristicscorresponding to the recording conditions shown in FIGS. 21B-21D,respectively;

FIG. 23A is a top plan view showing a magnetic head;

FIG. 23B is a sectional view taken along line 23B--23B in FIG. 23A;

FIG. 24A is a top plan view showing another embodiment of a magnetichead;

FIG. 24B is a sectional view taken along line 24B--24B in FIG. 24A;

FIG. 25 is an exploded perspective view showing an embodiment of amagnetic disc cassette applicable to an apparatus according to thepresent invention;

FIGS. 26A and 26B are a top plan view and a side view showing thecassette when the shutter is closed, respectively;

FIGS. 26C and 26D are a top plan view and a side view of the cassettewhen the shutter is opened, respectively;

FIG. 27 is a sectional view, on enlarged scale, taken along line 27--27in FIG. 26A; and

FIG. 28 is a perspective view used to explain the opening operation ofthe shutter.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIGS. 1 and 2 show one embodiment of a magnetic recording and/orreproducing apparatus for the case in which the present invention isapplied to such an apparatus. Here, a magnetic disc recording and/orreproducing apparatus is assembled on a chassis 1 as a base. The chassis1 is mainly formed of a frame having a U shape and has two upright sideplates 2. Guide slots 3 and 3 are formed at opposite positions of theside plates 2 and 2 and are extended downward from the upper edges ofthe side plates 2 and 2. The guide slots 3 and 3 are in an opposedrelationship with each other and are adapted to receive therein rollersprojected from a cassette guide to be described below.

Guide slots 4 and 4 are horizontally elongated between the guide slots 3and 3 in the side plates 2 and 2 and are in an opposed relationship witheach other between the guide slots 3 and 3. In the front edges of theside plates 2 and 2, guide-slots 5 and 5 are horizontally extended.These guide slots 4 and 4 and the guide slots 5 and 5 are adapted toreceive therein guide rollers of a slide frame to be described below.

Three positioning pins 7, 7 and 7 are extruded upright from a bottomplate 6 of the chassis 1 at predetermined positions.

These pins 7, 7 and 7 are used to vertically position a cassette to bedescribed below.

A pulse motor 8 for displacing a magnetic head is secured on one side ofthe bottom plate 6 of the chassis 1 by studs 8a and 8a. A projection 9is cut and protruded from the bottom plate 6 adjacent to the pulse motor8 and has a hole 10. On one of the side plates 2 and 2, a hole 11 isformed which is in an opposed relationship with the hole 10 of theupright projection 9. These holes 10 and 11 are used to mount a guideshaft 12 which guides a head mounting base to be described below.

A guide bar 13 is extended in parallel with the guide shaft 12 betweenthe side plates 2 on the front side of the chassis 1.

The output shaft of the pulse motor 8 which extends downwardly carries adrive gear 14 which in turn is in mesh with a gear 15 rotatably mountedon the bottom plate 6.

An aperture 16 is formed substantially at the center of the base plate 6and is adapted to receive therein a boss 17 which supports a magneticdisc drive mechanism.

As shown in FIG. 3, the boss 17 has a flange 17a extended radiallyoutwardly from the central portion thereof. The boss 17 is stacked onthe bottom plate 6 with the lower portion of the boss 17 being insertedinto the aperture 16 and the flange 17a of the boss 17 is securelyattached to the bottom plate 6 with screws 18 and 18.

A rotary shaft 20 is rotatably supported by a pair of bearings 19 and 19which are vertically spaced apart within the boss 17. A collar 21 isinterposed between the bearings 19 and 19. The outer rings of thebearings 19 and 19 are pressure-fitted into the boss 17.

A coupler 22 is securely fixed to the upper end of the rotary shaft 20and is adapted to engage with the center hub of a magnetic disc. Thecoupler 22 has a flange 22a into which a positioning pin 23 isvertically movably engaged.

The lower end of the pin 23 is securely fixed to a free end of a leafspring 24 on the lower surface side of the flange 22a, so that the pin23 is normally biased upward.

A spring 25 is loaded between the lower surface of the coupler 22 andthe inner ring of the upper bearing 19, so that the inner ring is biaseddownwardly. As a results, the inner ring is deviated relative to theouter ring, so that uniform contact between the inner and outer ringsand the bearing balls is ensured and consequently the play of the innerand outer rings can be eliminated. As a consequence, the rotary shaft 20is prevented from vibrating.

A gear 27 with a cam 26 formed over the upper surface thereof issecurely fitted through a boss 28 to the boss 17. The gear 27 is in meshwith the gear 15 so that the rotation of the pulse motor 8 istransmitted to the cam 26. A retaining ring 29 is fitted over the boss28 so that the cam 26 is prevented from being pulled out.

In FIGS. 1 and 2, reference numeral 30 denotes a head mount which is inthe form of an elongated plate. One end of the head mount 30 is slidablyengaged into the guide shaft 12 through a linear bearing 31 as shown inFIGS. 4 and 5A. The other end of the head mount 30, which is a free end,is supported by the other guide shaft 13 and is slidably guided.

As best shown in FIGS. 5C and 5D, a shaft 33 is extended downward fromthe free end of the head mount 30 and the shaft 33 rotatably carries aroller 32 in the form of a corn. A spring 34 is loaded between the shaft33 and the roller 32 so that the roller 32 is normally biased upwardly.

The shaft 33 is securely fixed to the head mount 30 by a screw 35. Oneend of a leaf spring 36 is also securely fixed to the upper side of thehead mount 30 by the screw 35.

The head mount 30 has an opening 30a which is covered by the leaf spring36. A roller 37 is rotatably engaged into the opening 30a and isperpendicular to the guide shaft 13.

As a result, the guide shaft 13 is elastically clamped between theconical surface of the roller 32 and the roller 37 so that the headmount 30 is slidable relative to the guide shaft 13.

As described above, the shafts 12 and 13 which guide the head mount 30are supported by the linear bearings and the bearing member whichutilizes rotary friction of the roller, so that wear can be reduced to aminimum. Accordingly, the head mount 30 can be displaced smoothly, ascompared with bearings utilizing sliding friction.

As a result, a pulse motor which is compact in size and light in weightwith a small power consumption and is therefore inexpensive can be usedas the pulse motor 8.

Alternatively, as shown in FIG. 5B, the guide shaft 12 may be supportedby bearing members 38 which utilize sliding friction. When the bearingmember 38 is made of a material such as ruby which is very expensive butexcellent in wear resistance, a compact and inexpensive pulse motor maybe used as the pulse motor 8.

A spring 39 is extended between the head mount 30 and the uprightprojection 9, so that the head mount 30 is normally biased to movetoward the rotary shaft 20.

The head mount 30 is disposed above the cam 26. A lever 40 has one endwhich is rotatably supported to the undersurface of the head mount 30 bya screw 41.

A spring 42 is extended between the other end of this lever 40 and thehead mount 30, so that the lever 40 is normally biased to rotate in thecounterclockwise direction in FIG. 1.

A roller 44 made of metal or a synthetic resin, but usually metal, isrotatably supported to the undersurface of the lever 40 by a pin 43 andis in engagement with the cam surface of the cam 26.

As shown in FIG. 6, the cam 26 is roughly in the form of a spiral as awhole and has a plurality of cam portions with a saw-tooth or step-likeshape. When a magnetic disc has 40 tracks, the cam 26 has 40 or more camportions corresponding to the number of tracks.

In FIG. 6, the cam portion is so designed that R₀ represents the maximumradius and R₃₉ represents the minimum radius. Therefore, a magnetic headcan move from the outermost track to the innermost track.

The cam 26 is rotated by the pulse motor 8. That is, the rotation of thepulse motor 8 is transmitted to the cam 26 through the gears 14, 15 and27.

For instance, the pulse motor 8 is so designed that in response to onedrive pulse, the pulse motor 8 rotates by 18°. When the drive pulse is apositive phase pulse, the pulse motor 8 is rotated clockwise, and whenthe drive pulse is a negative phase pulse, the pulse motor 8 is rotatedcounterclockwise.

The gear ratios among the gears 14, 15 and 27 are so determined thatwhen the pulse motor 8 rotates by 18°, the gear 27 is rotated by 6°, forexample. Within a range of this angle of 6°, 40 cam portions withrespective radii R₀ -R₃₉ are formed.

Therefore, every time that the cam 26 is rotated by 6°, a magnetic head47 is displaced by a distance equal to one track pitch. Moreparticularly, the magnetic head 47 is displaced by 0.12 millimeters mm,for instance, and the total displacement of the pitches of the 40 tracksis about 5 mm.

As shown in FIGS. 8A and 8B, an adjusting screw 45 is threadably engagedwith a downwardly bent portion 30c which is protruded from the headmount 30 in the middle of the longitudinal direction thereof. Theadjusting screw 45 is engaged with a downwardly bent portion 40a at thefree end of the lever 40. By tightening or loosening the adjusting screw45, the position of the lever 40 can be adjusted.

In the middle of the longitudinal direction of the head mount 30 formedis a longitudinally elongated opening 30b, as shown in FIG. 4, intowhich the magnetic head 47 is disposed by a supporting member 46.

An arcuate leaf spring 49 is provided between one end of the supportingmember 46 and an upright projection 48 extruded from one end of theelongated opening 30b. An adjusting screw 51 is threadably engaged withan upright projection 50 extended upwardly from the other end of theelongated opening 30b. The leading end of the adjusting screw 51 engageswith the other end of the supporting member 46 which is remote from thespring 49.

It follows, therefore, that the position of the supporting member 46 canbe adjusted by tightening or loosening the adjusting screw 51, so thatthe position of the magnetic head 47 can be adjusted. In other words,the displacement path of the magnetic head 47 relative to the center ofa magnetic disc can be correctly adjusted by the adjusting screw 51.

After the magnetic head 47 has been correctly adjusted by the adjustingscrew 51, the supporting member 46 is securely fixed to the head mount30 with screws 52, so that the magnetic head 47 is mounted to the headmount 30.

Brackets 53 and 53 are extended from the end of the head mount 30 on theside of the guide shaft 12 to rotatably support one end of a pad arm 54with a pin 55, as shown in FIGS. 1 and 4.

A torsional coil spring 56 is wound around the pin 55, so that the padarm 54 is normally biased to rotate in the clockwise direction in FIG.4.

The leading end of the pad arm 54 is extended to the space above themagnetic head 47. An adjusting screw 57 is threadably engaged with theleading end of the pad arm 54 in opposed relationship with the magnetichead 47. A pad 58 is attached to the lower end of the adjusting screw 57so as to push a magnetic disc toward the magnetic head 47.

Therefore, by tightening or loosening the adjusting screw 57, the degreeto which the pad 58 parallel to the magnetic head 47 and the padpressure can be adjusted.

A control plate 59 is formed integrally with the undersurface of thegear 27, as shown in FIG. 6, and has a projection 59a. A notch 59b isformed at the base of the projection 59a.

A lever 61 is pivotably fixed with a pin 60 to the base plate 6 adjacentto the control plate 59. The lever 61 has two projections 61a and 61bextended from one end of the lever 61 and spaced apart from each otherby a predetermined distance. These projections 61a and 61b are normallyin contact with the outer periphery of the control plate 59.

The other end portion of the lever 61 is elongated in the longitudinaldirection and is positioned to close the upper surface of a notch 6aformed at the edge on the front side of the base plate 6. A sensor 62 isdisposed in the notch 6a. The sensor 62 comprises, for instance, a lightemitting element and a light receiving element. The sensor 62 alwaysreceives light reflected from the lower surface of the other end of thelever 61 so as to monitor whether or not the lever 61 is located at apredetermined position. Further, the sensor 62 may be a light sensor ofthe light transmission type having light emitting and receiving elementsdisposed in opposed relationship on the respective sides of the surfacesof the lever 61. Alternatively, the sensor 62 may be of the magneticdetection type.

The position of the lever 61, the projection 59a of the control plate 59and the cam portion with the maximum radius R₀ of the cam 26 have thefollowing relationship.

That is, when the roller 44 reaches the cam portion with the maximumradius R₀ of the cam 26, the projection 59a of the control plate 59engages with the projection 61b of the lever 61.

Therefore, as shown in FIG. 6, when the roller 44 is in engagement withthe cam portion with the radius R₁ of the cam 26, the projection 61b ofthe lever 61 is released from the projection 59a of the control plate59, so that the other end of the lever 61 is positioned above the sensor62.

Under these condition, the projections 61a and 61b of the lever 61 arebrought into contact with the periphery of the control plate 59, so thatthe rotation of the lever 61 is prevented.

When the cam 26 is advanced by one step by the pulse motor 8, the roller44 rides over the cam portion with the maximum radius R₀, so that themagnetic head 47 and the head mount 30 are brought to a positioncorresponding to the outermost track.

In this situation, as shown in FIG. 7, the projection 59a of the controlplate 59 engages with the projection 61b of the lever 61, so that thelever 61 is rotated in the counterclockwise direction in FIG. 7 andconsequently the projection 61b of the lever 61 engages with the notch59b of the control plate 59. The other end of the lever 61 is,therefore, displaced away from the upper position of the sensor 62, sothat the sensor 62 is interrupted. As a result, it is detected that themagnetic head 47 has reached the outermost track.

Therefore, when the outermost track is referred to as "0" track and ifit is ensured that the position of the outermost track is detected bythe above-described mechanism and the magnetic head 47 is brought to theposition corresponding to the outermost track when a power supply isturned on, then the position of the magnetic head 47 corresponds to the"0" track at the time of starting. When, for instance, five pulses areapplied to the pulse motor 8, the magnetic head 47 is brought to theposition corresponding to the fifth track. When, for instance, tenpulses are applied to the pulse motor 8, the magnetic head 47 is broughtto the position corresponding to the tenth track and so on. Thus, anydesired track can be selected by applying a desired number of pulses tothe pulse motor 8 at the position of track "0".

The present position of the magnetic head 47 is stored in the memory ofa digital processing system by storing the number of such input pulses.

For instance, the control plate 59 and the lever 61 have the followingspecific dimensions.

As shown in FIG. 6, when it is assumed that the radius R of the controlplate 59 is R=15 mm and the rotation angle α per one step is α=6°, thenperipheral displacement δ of the control plate 59 is

    δ=tan 6°×15 mm≈1.6 mm.

If it is further assumed that the distance B between the pin 60 of thelever 61 and one end of the lever 61 is B=5 mm; the distance A betweenthe pin 60 and the other end of the lever 61 is A=13 mm; thedisplacement of the other end of the lever 61 is w₁ ; and the angle ofrotation of the lever 61 is α', then,

    α'=(15/5)×6°=18°

    δ.sub.1 ≈tan 18°×13 mm≈4.2 mm

Therefore, when the periphery of the control plate 59 is rotated by 1.6mm, the lever 61 rotates about 18° because the lever ratio of the lever61 is 3.

As a result, the other or outer end of the lever 61 is displaced by 4.2mm, which is sufficient to cover and uncover the sensor 62 whose size isassumed to be 3 mm.

While it is of course possible that if the sensitivity of the sensor 62is enhanced, a displacement of the order of 1.6 mm of the projection 59aof the control plate 59 can be satisfactorily detected, the lever 61 ofthe type described above can be employed to detect the displacement ofthe control plate 59 in a simple and inexpensive manner.

When this lever 61 is employed, the rotation of the control plate 59 andaccordingly the rotation of the cam 26 can be detected in the outerspace where no other parts exist. As a result, there can be provided adetection mechanism without limitation of space.

A magnetic disc can be loaded on the coupler 22 provided at the upperend of the rotary shaft 20.

Most magnetic discs are generally made of plastic or synthetic resinexcept for the center hub portion. On the other hand, a magnetic discdrive mechanism is mostly made of metal, so that there arises a problemdue to the difference between coefficients of thermal expansion.

This problem will be discussed by using a particular example. Referringnow to FIG. 8A, it is assumed that the distance between the axis of therotary shaft 20 and the center of the magnetic head 47 or a certaintrack is l₁ ; the distance between the periphery of a center hub 63 of amagnetic disc 64 and the axis of the rotary shaft 20 is l₂ ; and thedistance between the periphery of the center hub 63 and that track isl₃. Then, the portion l₂ is made of metal and the portion l₃ is made ofplastic. For instance, if l₁ =20 mm; and l₂ =8 mm, then l₃ is 12 mm.

Distance L₁ between the axis of the rotary shaft 20 and the track inquestion consists of distance L₂ between the axis of the rotary shaft 20and the periphery of the boss 28; distance L₃ between the boss 28 andthe center of ratational axis of roller 44; and distance L₄ between thecenter of ratational axis of the roller 44 and the track. Here, thevarious parts disposed along this distance L₁ are made of metal.

It is now assumed that L₂ =8 mm and L₄ =1.5 mm. Since L₁ =20 mm, L₃=20-8-1.5=10.5 mm.

It is now assumed that at 25° C. the error between L₁ and l₁ is madezero. When the temperature rises by 20° C. to 45° C., the followingproblem occurs.

It is further assumed that the coefficient of linear expansion of themetal is 16×10⁻⁶ mm/°C. and the coefficient of linear expansion of thesynthetic resin film is 17×10⁻⁵ mm/°C. The cam 26 is made of the metal,as in a conventional apparatus. Distances l₁ and L₁ are obtained from P₁(1+α₁ Wt), where α₁ is a coefficient of linear expansion and Wt is atemperature difference. The results are as follows: ##EQU1## That is,when the temperature rises by 20° C., the difference between L₁ and l₁becomes 20.043-20.006=37 μm. As a result, the data on the magnetic disc64 cannot be correctly read out.

Therefore, in the present embodiment of the present invention, the cam26 is made of a synthetic resin material such as polyethyleneterephthalate having a coefficient of linear expansion which is 17×10⁻⁵,that is, substantially the same to or similar to that of the magneticdisc 64. Then, ##EQU2## That is, by changing the material of the cam 26as described above, the difference between L₁ and l₁ becomes20.043-20.038=5 μm. Therefore, adverse effects due to the thermalexpansion can be eliminated to a satisfactory degree.

According to the present embodiment of the present invention, theposition of the magnetic head 47 relative to the center of the roller 44can be adjusted by the adjusting screw 45. Therefore, while inspectingthe position of the magnetic head 47 through a microscope or the like,L₁ can be exactly set to 20 mm.

FIG. 8B illustrates that the center of the magnetic head 47 is deviatedfrom the center of the roller 44 by δ.

Furthermore, the cam 26 is rotatable, so that, as shown in FIG. 8A,there exists clearance δ₁ and δ₂ between the bosses 17 and 28.

Therefore, when the cam 26 is rotated, the clearances δ₁ and δ₁ arealways varied, so that this variation directly influences distance L₁.

In order to eliminate this influence, according to the presentembodiment, the clearance δ₁ between the bosses 17 and 28 is alwaysmaintained to be zero. To this end, the spring 39 is expanded betweenthe head mount 30 and the projection 9, so that the head mount 30 isnormally biased toward the boss 28. The lever 40 is biased to be pressedagainst the adjusting screw 45 attached to the head mount 30 under theforce of the spring 42, so that the magnetic head 47 is prevented frombeing deviated from a track.

The rotary shaft 20 is extended downwardly through the bottom plate 6 ofthe chassis 1 and has a member, i.e., a coil 65a which constitutes amotor together with a printed circuit board 65 securely fixed to theundersurface of the bottom plate 6 of the chassis 1, as shown in FIG. 3.That is, the coil 65a is secured to the undersurface of the bottom plate6 of the chassis 1 via an insulation layer.

A boss 66 is fitted to the lower end of the rotary shaft 20. Asaucer-shaped yoke 68 and a gear 69 are securely fixed with screws 67 tothe boss 66. A ring-shaped permanent magnet 70 is securely disposed onthe yoke 68 in opposed relationship with the coil 65a. The permanentmagnet 70 is magnetized in the fashion of plural magnetic poles.

As shown in FIG. 1, a non-reflecting plate 71 of a small size issecurely attached to the outer periphery of the yoke 68 at apredetermined position of the yoke 68 and a sensor 72 for detecting thenon-reflecting plate 71 is securely attached to the printed circuitboard 65, so that the sensor 72 produces one pulse per one rotation ofthe yoke 68.

The yoke 68 is plated with nickel aluminum or the like, so that it isensured that the sensor 72 consisting of a light emitting element and alight receiving element can positively detect the existence of thenon-reflecting plate 71. Thus, the output signal derived from the sensor72 can be used as an index signal.

Reference numeral 73 denotes a sensor for detecting the rotational speedof the motor formed by the coil 65a, the yoke 68 and the permanentmagnet 70.

The sensor 73 is securely attached to the printed circuit board 65. Thesensor 73 includes a permanent magnet 74 and a yoke 75 for mounting thepermanent magnet 74. As shown in FIG. 3, the yoke 75 is disposed in thevicinity of the gear 69.

In FIGS. 1 and 3, reference numeral 76 represents an electronic partsuch as an LSI; and reference numeral 77 denotes screws for fixedlymounting the printed circuit board 65 on the chassis 1.

The gear 69 has a large diameter and is made of iron material. When theteeth of the gear 69 approach the yoke 75, magnetic flux is varied onthe side of the sensor 73, so that a current flows through the coil inthe sensor 73. This current can be derived as an output signal.

The above-described motor formed by the coil 65a, the yoke 78 and thepermanent magnet 70 drives to rotate a magnetic disc. This motor is sodesigned and constructed that it rotates at 300 rpm.

In order that the motor can rotate uniformly and constantly at apredetermined rotational speed of 300 rpm, the time period required forone rotation, i.e., 200 milliseconds ms is further divided so that thecorrect rotation control can be ensured.

More specially, the gear 69 has a diameter of 50 mm and a module of0.25, and the number of teeth is 200. In this case, variations inrotation of the motor can be monitored by the sensor 73 at a timeinterval of 200 ms÷200=1 ms.

The printed circuit board 65 is made of a thin insulating board and issecurely mounted on the iron or steel chassis 1. The magnetic fluxproduced when current flows through the coil 65a passes a magneticcircuit established between the chassis 1 and the yoke 68, so that thepermanent magnet 70 and, therefore, the yoke 68 and the gear 69 arerotated.

As described above, the printed circuit board 65 is fixed to the steelor iron chassis 1, so that it becomes possible to reduce the distancebetween the permanent magnet 70 and the chassis 1. As a result, theefficiency of the magnetic circuit is improved.

When the chassis 1 is made of an iron or steel plate and is alsoutilized to form a printed circuit board, it becomes possible to reducethe thickness of the motor by the thickness of the printed circuit board65 which constitutes the motor. Furthermore, the number of parts canalso be reduced.

Further, the permanent magnet 70 has a magnetic force attracting thechassis 1 toward the magnet 70, so that the inner ring of the lowerbearing 19 is forced upwardly by the boss 66. As a result, the play ofthe bearing 19 can be absorbed, so that oscillation or vibration of therotary shaft 20 can be prevented by the upper and lower bearings 19 and19.

The inner and outer diameters of the boss 17 which is securely attachedto the chassis 1 are machined with reference to the stationary portionof the chassis 1. Therefore, the inner and outer diameters of the boss17 can be machined with an accuracy of the order of 1-2 μm.

Because of this machining accuracy and the absorption of play by thebearings 19 and 19, the vibration of the rotary shaft 20 including theboss 17 can be maintained within 5 μm.

So far the drive mechanism has been described in detail and next a discloading mechanism will be described.

The disc loading mechanism in accordance with the present invention hasa construction as shown in FIGS. 9-16.

A sliding frame 78 has an opened bottom and opened front and rear sides.The sliding frame 78 rotatably carries rollers 79 and 79 and 79a and 79aon both sides thereof. These rollers 79 and 79 and 79a and 79a areslidably and rotatably fitted into the elongated slots 4 and 4 and theguide slots 5 and 5, respectively, which are formed on the side walls 2and 2 of the chassis 1.

The sliding frame 78 has openings 78a and 78a at the upper corners ofthe right and left sides thereof. Projections 78b and 78b are protrudedintegrally from the top surface of the sliding frame 78 and are extendedhorizontally over the openings 78a and 78a. Springs 80 and 80 areexpanded between the projections 78b and 78b and the projections 2a and2a protruded from the side walls 2 and 2 of the chassis 1. Consequently,the sliding frame 78 is normally biased toward the front side of thechassis 1.

Rollers 81 and 81 are rotatably supported by projections 78d and 78dprotruded from the lower ends of both the side plates of the slidingframe 78, so that the sliding frame 78 is slidable along the chassis 1by the rollers 81 and 81.

A push button 82 is securely attached to a projection 78c protruded fromone end of the sliding frame 78. Each of the right hand and left handside plates of the sliding frame 78 has two elongated holes 83 and 83which are inclined to the upper surface of the sliding frame 78 and arein parallel with each other. Sliding plates 84 and 84 are slidablydisposed over the inner surfaces of the right hand and left hand sideplates.

These sliding plates 84 and 84 are in the rectangular form and havelower ends in contact with shafts 81a and 81a with a small diameter ofthe rollers 81 and 81 which are in contact with the bottom plate 6 ofthe chassis 1.

Upright projections 84a and 84a extended from the upper side edges ofthe sliding plates 84 and 84 are fitted into the openings 78a and 78a ofthe sliding frame 78 as guide means. The sliding plates 84 and 84 haveinwardly directed projections 84b at the end thereof.

Each of the sliding plates 84 and 84 has a pair of L-shaped openings 85and 85 substantially in opposed relationship with the elongated openings83 and 83 of the sliding frame 78. Inwardly directed projections 84c and84c are protruded from the lower side edges of the sliding plates 84.Springs 86 and 86 are expanded between the projections 84c and 84c andthe sliding frame 78.

A cassette guide 87 is disposed under the sliding frame 78. The cassetteguide 87 is in the form of a flat frame and has right hand and left handrails 87a and 87a which serve as a guide to a cassette 93. The cassetteguide 87 has downwardly extended right and left projections 88 and 88and pins 89 and 89 are horizontally outwardly extended from theseprojections 88 and 88 to rotatably carry rollers 90. The respectiverollers 90 and 90 are rotatably fitted into the L-shaped openings 85 and85 of the sliding frames 84 and the elongated holes 83 and 83 of thesliding frame 78.

The upper surface of the cassette guide 87 has an opening 87b at thecenter thereof. A frame 91 is integrally formed on the upper surface ofthe cassette guide 87 in such a way that the frame 91 bridges theopening 87b. The frame 91 is provided with a hub holder 92.

The cassette guide 87 has an opening 87c adjacent to the opening 87bthrough which the magnetic head 47 is exposed.

The above-described sliding frame 78, the two sliding plates 84 and 84and the cassette guide 87 constitute the cassette loading mechanism.

Next, the operation of the cassette loading mechanism will be described.

Prior to the loading of a magnetic disc cassette 93, the sliding frames78 and 78 are displaced rightward in FIGS. 9 and 14 by the forces of thesprings 80 and 80.

Under these conditions, the rollers 90 and 90 are fitted into the guideslots 3 and 3 of the side plates 2 and 2 and, as shown in FIG. 14, arein contact with the upper ends of the elongated holes 83 and 83.Furthermore, it is seen that the rollers 90 and 90 are engaged with thehorizontal portions 85a and 85a of the L-shaped openings 85 and 85. Thatis, movement of the rollers 90 and 90 is restricted by the guide slots 3and 3, the elongated holes 83 and 83 and the L-shaped openings 85 and85.

The sliding plates 84 and 84 are biased rightward in FIG. 14 by theforce of the springs 86 and 86 and the cassette guide 87 is ready toreceive the cassette 93 while the cassette guide 87 is positioned at anupper position defined by-the horizontal portions 85a and 85a of theL-shaped openings 85 and 85.

When the cassette 93 is engaged with the rails 87a and 87a of thecassette guide 87 and then inserted inside under these conditions, thecassette 93 is guided by the rails 87a and 87a and led into the cassetteguide 87.

In the meantime, the leading edge of the cassette 93 engages with theinwardly protruded projections 84b and 84b at the leading edges of thesliding plates 84 and 84, so that the sliding plates 84 and 84 arecaused to advance forwardly against the force of the springs 86 and 86.

As the sliding plates 84 and 84 are displaced, the L-shaped openings 85are also displaced, so that, as shown in FIGS. 13A and 13C, the rollers90 and 90 which have been located in the guide slots 3 and 3 and thehorizontal portions 85a and 85a of the L-shaped openings 85 and 85 dropinto the vertical portions of the L-shaped openings 85 and 85. As aresult, the guide rollers 90 and 90 are displaced downwardly in theguide slots 3 and 3 and the vertical portions of the L-shaped openings85 and 85, as best shown in FIGS. 13B and 13D. That is, the cassette 93is displaced downwardly together with the cassette guide 87.

When the cassette 93 is being inserted, the rollers 90 and 90 which arelocated at the upper ends of the elongated holes 83 and 83, as shown inFIG. 13E are displaced downwardly in the elongated holes 83 and 83, asbest shown in FIG. 13F.

In the case of the displacement of the rollers 90 and 90, the rollers 90and 90 push the right hand edges of the elongated holes 83 and 83, sothat the sliding frame 78 is displaced rightward by a predetermineddistance, as shown in FIG. 15.

When the cassette 93 as well as the cassette guide 87 are displaceddownwardly in the manner described above, the two projections 7a and 7aof the two positioning pins 7 and 7 having the projections 7a and 7a ofthe three positioning pins 7 and 7 and 7 are fitted into two positioningholes 93a and 93a of the cassette 93, while the upper end of the pin 7having no projection 7a engages with the undersurface of the cassette93, so that the cassette 93 is held in position at a predeterminedheight, as shown in FIG. 12.

In this case, as best shown in FIG. 12, the coupler 22 engages with thecenter hub 63 of the magnetic disc 64 and the pin 23 is fitted into apositioning hole 96 of the center hub 63. The hub holder 92 is pressedagainst the upper surface of the center hub 63. This loading operationof the cassette 93 is carried out, while the rotary shaft 20 isrotating.

After the cassette 93 has been set in the manner described above, themechanism is ready to record or reproduce information.

In order to unload the loaded cassette 93, the push button 82 isdepressed. Then, the sliding frame 78 advances, so that the peripheriesof the inclined elongated slots 83 and 83 push the rollers 90 and 90upwardly. As a result, the cassette guide 87 is also pushed upwardly toreturn to its initial position.

When the cassette guide 87 is lifted so that the rollers 90 and 90 arealso lifted, the rollers 90 and 90 are brought to the upper positions ofthe L-shaped openings 85 and 85. As a result, under the tensile force ofthe springs 86 and 86, the sliding plates 84 and 84 are displacedrightward as shown in FIG. 14, so that the rollers 90 and 90 engage withthe horizontal portions 85a and 85a of the L-shaped openings 85 and 85.As a result, the inwardly extended projections 84b and 84b push thecassette 93, so that the cassette 93 is pushed forwardly from the edgeportion of the cassette guide 87. Thus, the cassette 93 can be takenout.

After the sliding frame 78, the sliding plates 84 and 84 and thecassette guide 87 are first assembled as shown in FIG. 16, the cassetteloading mechanism thus assembled is disposed inside the side plates 2and 2 of the chassis 1, while the rollers 79 and 79 and 79a and 79a arefitted into the guide slots 4 and 4, and the guide slots 5 and 5,respectively. Next, the side plates 2 and 2 of the chassis 1 aresecurely fixed to the side surfaces of the sliding frame 87 by screws79b and 79b and 79d and 79d. Thus, the drive mechanism and the cassetteloading mechanism can be assembled in a simple manner. Finally, the padarm 54 is attached to the head mount 30.

FIG. 20A shows the block diagram of a control circuit in the magneticdisc recording and/or reproducing apparatus of the present embodiment.

The magnetic disc recording and/or reproducing apparatus of the presentembodiment in accordance with the present invention is controlled by acomputer 100 which is coupled to the magnetic disc recording and/orreproducing apparatus via lines; i.e., 34 input and output lines.

These 34 input and output lines are all controlled by digital signals.

The control circuit for the magnetic disc recording and/or reproducingapparatus comprises a digital processor 101 which is adapted to couplethe computer 100 to the magnetic disc includes various interfaces andrecording and/or reproducing apparatus and to amplify the output signalsfrom the sensors 62, 72 and 73 of the magnetic disc recording and/orreproducing apparatus which are converted into digital signals. Thedigital processor 101 also includes a pulse motor drive circuit fordriving the pulse motor 8 for bringing the magnetic head 47 to a desiredtrack.

Connected to the digital processor 101 are a read amplifier 102 foramplifying the data read out by the magnetic head 47, a write amplifier103 for amplifying the data to be written in the magnetic head 47, aread/write selection switch 104, an index amplifier 105 for amplifyingthe output from the sensor 72 which generates one pulse signal everytime that the magnetic disc 64 makes one rotation, a track positiondetection amplifier 106 for amplifying the output from the sensor 62which detects the "0" track position of the magnetic head 47 and a motordrive circuit 107 for driving the motor (65a, 70, 68) for rotating themagnetic disc 64.

The control circuit further includes a speed control circuit 108 forcontrolling the rotational speed of the disc rotating motor (65a, 70,68). The speed control circuit 108 is connected to the motor drivecircuit 107. The speed control is carried out in response to the signalstransmitted through signal lines 109 and 110 from the digital processor101, as will be described in more detail hereinafter.

The control circuit further includes an amplifier 111 for amplifying theoutput from the sensor 73 for monitoring the rotational speed of thedisc rotating motor (65a, 70, 68). Further, reference numeral 112denotes a television receiver, which is coupled to the digital processor101.

In the present embodiment, while the disc rotating motor can be rotatedat the same speed between recording and reproduction, as a matter ofcourse, the rotational speed of the disc rotating motor can be variedbetween recording and reproduction in order to record information at ahigh density and to improve reliability.

For that purpose, when a recording instruction is applied from thecomputer 100 to the digital processor 101, the digital processor 101applies a signal to the read/write selection switch 104, so that themagnetic head 47 is switched from the reproduction mode to the recordingmode. At the same time, the write amplifier 103 is energized.

A low speed rotation instruction is transmitted from the processor 101to the speed control circuit 108 through the signal line 110. The speedcontrol circuit 108 confirms that the intervals of the signalstransmitted from the amplifier 111 coincides with a speed controlinterval and thus judges a low speed rotation mode. Thereafter,recording information is applied to the magnetic head 47 from thecomputer 100 via the processor 101 and the write amplifier 103, so thatthe recording information is recorded on the magnetic disc.

On the other hand, when the computer 100 transmits a reproductioninstruction, the read write selection switch 104 is switched to the readmode and the read amplifier 102 is energized. The speed control circuit108 is switched to a high speed mode in response to the signaltransmitted to the speed control circuit 108 from the processor 101through the signal line 109. After the speed control circuit 108confirms that the disc rotating motor is switched to the high speedrotation mode through the amplifier 111, the readout operation of thedata stored in the magnetic disc is started and the data thus read outis inputted to the computer 100.

In the case in which it is desired that the recording and reproducingoperations are performed at the same rotational speed, it is sufficientthat a reference frequency for setting a reference high speed rotationof the speed control circuit 108 is set to the same frequency as in thecase of the low speed rotation mode.

FIG. 20B shows the output characteristic of the magnetic head 47 whendata is read out by changing the rotational speed of the magnetic disc64 from 300 rpm to 600 rpm.

It is assumed that at original point P, the output from the magnetichead 47 was adjusted to be 0.8V when the recording signal frequency wasf=125 kHz and the rotational speed of the magnetic disc 64 is 300 rpm.Then, when the rotational speed was doubled to 600 rpm, point Q wasobtained at which the output from the magnetic head 47 was substantiallydoubled.

When the recording signal frequency was doubled to 250 kHz, the magneticrecording density was increased so that point S was obtained at whichthe output from the magnetic head 47 was decreased by about 25%. Whenthe rotational speed was doubled under these conditions, point R wasobtained at which the output was doubled.

Accordingly, when the magnetic recording operation is carried out at thesignal frequency of 250 kHz while the magnetic disc 64 is rotating at300 rpm and when the reproducing operation is carried out at the samerotational speed, the output of 0.6V is obtained as shown at point S.However, when the rotational speed is set at 600 rpm in the case ofreproduction, the output of 1.2V can be obtained as indicated by pointR.

That is, an output voltage which is higher by 0.6V can be obtained.Therefore, a satisfactorily high output voltage for digital processingcan be obtained, and thus reliability can be improved even when theoutput is decreased due to variations in magnetic discs and losses inthe magnetic circuit of the magnetic head 47.

In the case in which the video signal of the television receiver 112 isrecorded on the magnetic disc 64, it is assumed that the rotationalspeed of the magnetic disc 64 is set to 3600 rpm, for example. Then, thepicture or video signal of one field in the NTSC system can be recordedon one track.

In the case of recording the television video signal on the magneticdisc 64, the maximum recording signal threshold frequency is about 6.1MHz. Therefore, it follows that if the rotational speed is increased by3600 rpm÷300 rpm=12 times higher as described with reference to FIG.20B, the output would increase. However, the recording signal frequencybecomes 6.1 MHz÷250 kHz=24 times, so that the recording density isincreased and the amplifier output becomes about 0.4 -0.5V. As aconsequence, it is ensured that the television video signal can berecorded or reproduced on and from the magnetic disc 64, if the magneticdisc 64 is rotated at such a high rotational speed.

Electronic parts which constitute the control circuit as shown in FIG.20A are mounted on the three printed circuit boards 65, 113 and 114 asshown in FIGS. 18 and 19.

The circuits relating to the index detection, the track positiondetection and the motor drive are mounted on the printed circuit board65.

The read/write selection switch 104 and the read and write amplifiers102 and 103 are mounted on the printed circuit board 113, while thecircuits associated with interfaces for processing the signals from theprinted circuit boards 65 and 113 are mounted on the printed circuitboard 114.

The printed circuit boards 65 and 113 are provided with femaleconnectors 115 and 115, while the printed circuit board 114 is providedwith male connectors 116 and 116 for connection with the connectors 115and 115, so that the printed circuit boards 65, 113 and 114 can beelectrically interconnected in a simple manner.

As shown in FIG. 19, the printed circuit boards 65, 113 and 114 aremounted on the upper, lower and side surfaces, respectively, of thechassis 1, so that the adjustments and confirmation of electricalsignals can be easily made from the exterior of the chassis 1 in a verysimple manner. Thus, if any circuit is broken or fails, it can berepaired in a very simple manner merely by replacing the associatedprinted circuit board.

The magnetic disc recording and/or reproducing apparatus can be used asa memory for the computer. In this case, various electric and electroniccomponents such as the cathode ray tube, power supply transformer, motorand so on which produce strong magnetic fields are disposed around themagnetic disc recording and/or reproducing apparatus. Therefore, it isnecessary that the magnetic disc recording and/or reproducing apparatusis protected from such magnetic fields.

In view of the circumstance, in the present embodiment, the chassis 1 isshaped in the form of U and the upper and side surfaces of the chassis 1are covered with the iron sliding frame 78, the iron sliding plates 84and the iron cassette guide 87 so that the magnetic disc recordingand/or reproducing apparatus is satisfactorily shielded from externalmagnetic fields.

FIGS. 21A-21D are schematic views used to explain the tracks of themagnetic disc 64. While in FIG. 21A, only eight tracks are illustrated,the magnetic disc 64 can actually have as many as 40 tracks.

FIG. 21B shows, on enlarged scale, three tracks "0", "1"and "2". Thetrack width a is 50 μm; the track gap b between the adjacent tracks is70 μm; and accordingly the track pitch is a+b=120 μm.

When the track gap b is greater than the track width a like thisexample, 40 tracks can be increased to 80 tracks so that the recordingcapacity can be doubled, if the data can be recorded between the tracks.

FIG. 21C, shows that the recording capacity is doubled in the mannerdescribed above. In FIG. 21C, the track width a ≅50 μm; the track gapb'=10 μm; and accordingly the track pitch a+b≅60 μm.

However, when the track gap b is decreased, it is likely thatinterference of magnetic recording occurs between the adjacent tracks.In view of this, in the present embodiment, two magnetic heads havingdifferent azimuths are used, as shown in FIG. 21D, so that the recordingdirections are changed alternately.

FIG. 22A shows the reproduction output voltage obtained from themagnetic head 47 as it was shifted radially at 10 μm interval from theouter periphery to the center of the magnetic disc 64 shown in FIG. 21D.

The reproduction output voltage was obtained by measuring the outputfrom the read amplifier 102. The reproduction output voltage is to beapplied to the digital processor or 101 to produce a peak-to-peak pulseof 5V voltage of TTL level which is applied to the computer 100.

Therefore, when the input threshold level is set to 0.4V in the case ofapplying the output as shown in FIG. 22A to the digital processor 101and thus it is so arranged that when the input exceeds 0.4V a pulse isgenerated, but when the input is less than 0.4V no pulse is generated, anormal digital signal can be obtained, even if the deviation between thecenters of the track and the magnetic head 47 becomes 25 μm, as shown inFIG. 22A.

It follows, therefore, that the total sum of the dimensional tolerancesdue to vibration or fluctuation of the motor shaft 20, an error in theradius of the cam 26 and expansion or contraction in the magnetic disc64 due to temperature and humidity variations that may be permitted isas much as ±25 μm.

FIG. 22B illustrates the output when the data is reproduced from thedouble-density tracks shown in FIG. 21C. In FIG. 22B, curve Aillustrates the output characteristic of track "0" when no data isrecorded on track "1" and curve B illustrates the output characteristicof track "1" when no data is recorded on track "0".

When information is recorded on tracks "0" and "1" and the measurementis made by displacing the magnetic head 47 from track "0" to track "1",the output is reproduced as indicated by curve C between curves A and B.This means that interference occurs between information on the adjacenttracks.

When the voltage of the hatched area surrounded by curves A, B and C ismeasured, it is seen that curve C does not correspond to the perfect sumof curves A and B, but curve C includes other noise components.Therefore, curve C does not represent correct information.

In this case, as shown in FIG. 22B, the limit of the deviation between atrack and the magnetic head 47 is about one half of 25 μm shown in FIG.22A; that is, ±12 μm. Therefore, the input level to the digital circuitmust be set to 0.65V.

That is, when the recording system as shown in FIG. 21C is employed soas to double the density of recorded information, the dimensionaltolerances must be improved by more than a factor of two. For thispurpose, parts must be machined with a higher degree of accuracy andaccordingly such parts are very expensive.

In view of the above, in the present embodiment, the magnetic recordingsystem as shown in FIG. 21D is employed. That is, recording is made byemploying a magnetic head having gaps of different azimuths whosedirections are set at θ₁ =θ₂ in the different directions alternately forthe adjacent tracks. In this embodiment, θ₁ =θ₂ =10°.

An embodiment of a structure of a magnetic head for carrying out theabove-described magnetic recording system is shown in FIGS. 23A and 23B.In FIG. 23A, reference numerals 117 and 118 denote core halvesconstituting one magnetic head core. When these core halves 117 and 118are abutted against each other, a gap G₁ with an angle of θ₁ is formed.Reference numerals 119 and 120 denote core halves constituting the othermagnetic head core. When these core halves 119 and 120 are abuttedagainst each other, a gap G₂ with an angle of θ₂ is formed.

These cores are supported by a core support 121 and coils 122 are woundaround the core halves 117 and 119.

The core support 121 can be made of a plastic including a large amountof glass material having a coefficient of expansion substantially equalto that of a glass member 123 having a thickness of b' and used to bondthe cores or to that of Sendust which may be a material of the core, sothat the core support 121 can satisfactory withstand environmentalvariations such as vibration, temperature variations and the like.

The output characteristic as indicated by curve A in FIG. 22C isobtained when the same information is recorded on tracks "0"-"2" andwhen the reproduced output voltage is measured by shifting the magnetichead consisting of the core halves 117 and 118 as shown in FIGS. 23A and23B at an interval of 10 μm from the outermost track toward the innertracks.

Characteristic curve A exhibits a low output voltage at track "1"because information is recorded on track "1" by means of the magnetichead with a gap inclined by θ₂.

That is, the gap used for recording information on track "1" isdifferent from the gap of the head, which is now passing, by 20°, sothat the output is low while the noise components are increased.

On the other hand, the output characteristic curve B as indicated by thebroken line in FIG. 22C is obtained when the head consisting of the corehalves 119 and 120 is shifted from the outermost track to the innertracks. In this case, the most optimum reproduction output voltage isobtained at track "1".

As described above, magnetic recording and reproduction operations arecarried out in such a way that the azimuth head with a gap inclined byθ₁ is used to trace the tracks with even numbers including 0, while theazimuth head with a gap inclined by θ₂ is used to trace the tracks withodd numbers. As a result, interference between magnetically recordedinformation between the adjacent tracks can be reduce to a minimum.

It follows, therefore, that if the input level is set to 0.4V, thedeviation between the recorded track and the magnetic head is permittedto be as much as 25 μm.

As described above, when information is recorded at a high density withthe magnetic head whose gaps have a gap angle θ directed in the oppositedirection, mechanical dimensional tolerances can be made broader, sothat the magnetic recording and/or reproducing apparatus can be madesimple in construction and consequently the design of the apparatus maybe much facilitated. Furthermore, compatibility of magnetic recordingmedia may be remarkably improved.

FIGS. 24A and 24B are schematic views used to explain another embodimentof a construction of the magnetic head. In this embodiment, two pairs ofmagnetic core halves 125 and 126 are mounted on a head mount 127. Thecore halves 125 and 126 are spaced apart from each other by apredetermine distance b".

The core halves 125 and 126 are 50 μm in thickness and the distance b"is2.5 mm. The core halves 125 and 126 are made of Sendust. A gap G=0.1 μmis made by melted glass. A coil 128 is wound around a winding window129.

When the magnetic head with the above-described structure is used tocarry out the magnetic recording system as illustrated in FIG. 21B, thecore halves 125 are used to record and reproduce information on and fromtracks "0"-"19", while the core halves 126 are used to record andreproduce information on and from tracks "20"-"39".

Therefore, in order that information is recorded into and reproducedfrom 40 tracks by means of the magnetic head 124 of the type describedabove, it is sufficient that the head mount 12 is displaced by 20 stepsby means of the pulse motor 8. In this case, it is apparent that it issufficient that the cam 26 has only 20 cam surfaces.

For instance, if a magnetic head has a single core and the core tracksthe tracks "0"-"°", then the tracking time becomes 20×3 ms=60 ms,because the speed characteristic of the pulse motor is 3 ms per track.

Even when the magnetic head is brought to the 20th track, the pulsemotor 8 does not immediately stop and is slightly oscillating.Therefore, the recording and reproducing operations must be carried outafter the pulse motor 8 has completely stopped. Therefore, the recordingand reproducing operations must started after about 70 ms.

If the magnetic head of the type as shown in FIGS. 24A and 24B is used,the recording or reproducing operation on or from track "20" can startimmediately after the recording or reproducing operation on or fromtrack "0" without a waiting time.

In the case of a magnetic head with a single core, the time required foraccomplishing the recording or reproducing operation of tracks "0"-"39"is 3 ms×39+10 (waiting time)=127 ms. In contrast, if the magnetic headof the type described with reference to FIGS. 23A and 23B or 24A and24B, the time required is 3 ms×19+10 (waiting time)=67 ms. Thereforethere is a time difference of 60 ms between these times, so that therecording or reproducing operation can be carried out at a high speed.

Referring next to FIG. 25, a magnetic disc cassette which can be used inthe magnetic disc recording and/or reproducing apparatus in accordancewith the present embodiment will be described.

As shown in FIG. 25, the cassette 93 comprises upper and lower cassettehalves 130 and 131. A magnetic disc 64 with the center hub 63 isinterposed between the upper and lower halves 130 and 131. Each of thecassette halves 130 and 131 has an opening 132 corresponding to thecenter hub 63 of the magnetic disc 64 and a head and pad window 133.

An arrow 134 indicates the direction of cassette insertion. A label 136in which the name of a recorded program is filled may be bonded to thebottom of a recess 135.

The projections 7a and 7a extended upwardly from the upper ends of thepins 7 and 7 are fitted into positioning holes 93a and 93a.

A shutter 139 which is U-shaped in cross section is fitted to theoutside of the cassette halves 130 and 131. That is, the shutter 139 isslidably fitted over the cassette 93.

The shutter 139 has a projection 141 on one side thereof which isslidably engaged with a groove 140 formed on the upper surface of theupper cassette half 130. The shutter 139 also has a projection 142 whichis bent inwardly in opposite to the projection 141. The projection 142is slidably engaged with grooves 143 and 144 formed on the innersurfaces of the upper and lower cassette halves 130 and 131, therebyguiding the shutter 139.

A pin 145 is extended upwardly at the innermost end of the groove 144 ofthe lower cassette half 131. A spring 146 is provided between theprojection 142 of the shutter 139 and the pin 145, so that the shutter139 is normally biased toward the center of the cassette 93.

Along the side edges of the grooves 143 and 144 of the cassette halves130 and 131 stepped portions 147 and 147, respectively, are formed so asto guide the projections 142 along the side edge of the grooves 143 and144.

The outer surfaces of the cassette halves 130 and 131 have rectangularrecesses 148 and 148, for receiving the shutter 139, respectively.

The upper and lower cassette halves 130 and 131 have stepped portion 149and 149 functioning as a stopper, respectively, for preventing theshutter 139 from being pulled out of the cassette 93.

The upper and lower cassette halves 130 and 131 have grooves 150 and150, respectively, for allowing the projection 87d protruded from theinlet end of the cassette guide 87 (see FIG. 9) to pass therethrough sothat the projection 87d opens the shutter 139 upon the insertion of thecassette 93 into the cassette guide 87, as shown in FIG. 28.

As shown in FIGS. 27 and 28, when the cassette 93 is inserted, theprojection 87d engages with the side edge 139a of the shutter 139, sothat the shutter 139 which has closed the head window 133 is opened.

FIGS. 26A and 26B show the case that the shutter 139 is closed, whileFIGS. 26C and 26D show the case that the shutter 139 is opened.

The magnetic disc cassette which is to be used in the magnetic discrecording and/or reproducing apparatus in accordance with the presentembodiment is designed and constructed as described above, so that theshutter which is normally closed is automatically opened by merelyinserting the cassette 93 into the cassette guide 87 on the side of themagnetic disc recording and/or reproducing apparatus. Therefore, thestart of the recording or reproducing operation is ensured.

As described above, according to the present embodiment of a magneticdisc recording and/or reproducing apparatus in which a magnetic disccassette containing a magnetic disc provided with a center hub is loadedso that the center hub engages with a rotary shaft of a disc rotatingmotor to rotate the magnetic disc, a cam as a rotation reference fordisplacing a magnetic head is fitted to the outer periphery of a bosssupporting a bearing which in turn supports rotatably the rotary shaft,so that the force from the cam can be transmitted to the magnetic headthrough a bearing utilizing the rotational movement having a hightransmission efficiency. As a result, a pulse motor for displacing themagnetic head can be made compact in size and light in weight and thepower consumption of the pulse motor can be reduced.

Furthermore, the cam is interposed between the level of the magnetichead and the chassis and the rotary shaft of the disc rotating motor isused also as the rotation center for the cam via a bearing mechanism, sothat the magnetic head can access any position. As a result, thepositioning mechanism can be disposed in a small space, so that themagnetic disc recording and/or reproducing apparatus can be made incompact in size and light in weight.

As described above, a head mount for mounting the magnetic head issupported by bearings with an extremely small rolling friction. As aresult, the magnetic head can be displaced with a low load, so that notonly the cam but also the pulse motor can be made compact in size andlight in weight. As a consequence, the magnetic disc recording and/orreproducing apparatus in accordance with the present embodiment may beprovided at a relatively low cost.

The position of the magnetic head can be adjusted not only in the axialdirection of the drive shaft of the disc rotating motor but also in theplane perpendicular to the axial direction of the drive shaft. Inaddition, the member for pressing the magnetic disc to the magnetic headcan be adjusted in the axial direction of the disc rotating motor.Therefore, the deviation between the head mount and the head chip aswell as the extremely small dimensional error due to play in thebearings of the head mount can be correctly adjusted in a simple manner.As a result, the reliability of the magnetic disc recording and/orreproducing apparatus of the present embodiment can be remarkablyimproved.

Moreover, the coefficient of linear expansion of the material of amagnetic disc is substantially equal or similar to that of the materialof the cam for displacing the magnetic head, so that there is anadvantage in that a deviation does not occur between the magnetic headand a track due to temperature variation.

Furthermore, a projection is formed integrally with the cam fordisplacing the magnetic head and there is provided a lever which isactuated by this cam. In response to the movement of the lever, a "0"track sensor is energized, so that the movement of one end of the levercan be increased by scores of times by utilizing the lever ratio. As aresult, even though the structure is very simple, the outermost trackcan be detected with an extremely high accuracy.

What is claimed is:
 1. A cassette loading apparatus for loading ordischarging a cassette containing a recording medium, said apparatuscomprising:(A) recording and/or reproducing means for recording data onor reproducing data from a recording medium contained in said cassette;(B) a base including said recording and/or reproducing means; (C) asupport member, formed by perpendicularly bending both side of saidbase, having a guide portion which engages with engagement pins formedat a side surface of a cassette holder for holding said cassette, saidsupport member for supporting said cassette holder to be verticallymovable along said guide portion; (D) a sliding member, which isdisposed to be slidable in an inserting or discharging direction of saidcassette into or from said cassette holder for holding said cassette,engages with said engagement pins provided at the side surface of saidcassette holder, and is provided with engaging portions formed ofengagement slanted surfaces for vertically moving said cassette holderin response to a sliding movement of said sliding member; (E) urgingmeans for urging said sliding member from a first position where saidcassette holder is moved to ascend, to a second position where saidcassette holder is moved to descend; (F) a lock member, movably providedin said inserting or discharging direction, for moving said slidingmember against the urging force of said urging member from said secondposition to said first position so that said sliding member locks atsaid first position and for releasing said locking state responsive tothe insertion motion of said cassette into said cassette holder so thatsaid sliding member is movable from said first position to said secondposition by means of the urging force of said urging means; and whereinsaid cassette holder is mounted to said sliding member in a state inwhich said engagement pins are respectively engaged with said engagingportions of said sliding member and said lock member is mounted on saidsliding member to form a cassette loading unit assembly, and saidcassette loading unit assembly is mounted on said base from theupperside of said base.
 2. An apparatus according to claim 1, whereinsaid recording medium is a magnetic disc rotatably mounted in saidcassette, and said recording and/or reproducing means is a magnetichead.
 3. An apparatus according to claim 1, wherein said recordingand/or reproducing means is supported for movement in a direction atright angles to said inserting or discharging direction.
 4. An apparatusaccording to claim 1, wherein said sliding member is further providedwith an operation button at a front end portion thereof, said slidingmember being slidable in said insertion or discharging direction bymanual operation of said operation button.
 5. An apparatus according toclaim 1 which further comprises a coil spring, said coil spring urgingsaid lock member in the discharging direction of said cassette, andwherein said lock member is slid by an urging force of said coil springto engage the engagement pins of said cassette holder to hold saidcassette holder at an ascended position when said sliding member is slidin the insertion direction.
 6. An apparatus according to claim 5,further comprising:shutter opening means for opening a shutter of saidcassette in response to an insertion of said cassette into said cassetteholder.
 7. A recording medium loading apparatus for loading or ejectinga recording medium, said apparatus comprising:(a) recording and/orreproducing means for recording data on or reproducing data from arecording medium; (b) a base including said recording and/or reproducingmeans, said base having a first side, a second side and an upper side;(c) a support member, said support member being formed byperpendicularly bending the first and second sides of said base, havinga guide portion which engages with engagement pins formed at a sidesurface of a holder for holding said recording medium, and supportingsaid holder for vertical movement along said guide portion; (d) asliding member, said sliding member being slidable in an inserting orejecting direction of said recording medium into or from said holder forholding said recording medium, engaging with said engagement pinsprovided at the side surface of said holder, and being provided withengaging portions formed of slanted surfaces for vertically moving saidholder in response to a sliding movement of said sliding member; (e)urging means for urging said sliding member from a first positionwherein said holder is moved to ascend, to a second position where saidholder is moved to descend; and (f) a lock member, said lock memberbeing movably provided in said inserting or ejecting direction forlocking said sliding member at said first position when said slidingmember is moved against the urging force of said urging member from saidsecond position to said first position, and for releasing said lockingstate responsive to the insertion motion of said recording medium intosaid holder so that said sliding member is movable from said firstposition to said second position by the urging force of said urgingmeans; wherein said holder is mounted on said sliding member in a statein which said engagement pins are respectively engaged with saidengaging portions of said sliding member and said lock member is mountedon said sliding member to form a recording medium loading unit assembly,and said recording medium loading unit assembly is mounted on said basefrom the upper side of said base.
 8. An apparatus according to claim 7,wherein said recording medium is a magnetic disc rotatably mounted in acassette, and said recording and/or reproducing means is a magnetichead.
 9. An apparatus according to claim 8, wherein said recordingand/or reproducing means is movably supported in a direction at rightangles to said inserting or ejecting direction.
 10. An apparatusaccording to claim 7, wherein said sliding member is further providedwith an operation button at a front end portion thereof, said slidingmember being slid in said insertion or ejecting direction by manualoperation of said operating button.
 11. An apparatus according to claim10, further comprising:shutter opening means for opening a shutter ofsaid cassette in response to an insertion of said cassette into saidcassette holder.
 12. An apparatus according to claim 7, wherein saidlock member is urged in a cassette ejecting direction by a coil spring,and said lock member is slid by an urging force of said coil spring tothe engagement pins of said cassette holder to hold said cassette holderat an ascended position when said sliding member is slid in theinsertion direction.
 13. An apparatus according to claim 7, wherein saidsliding member engages said engagement pins at a first side and a secondside of said holder.
 14. An apparatus according to claim 7, wherein saidurging means is provided on a first side and a second side of saidsliding member.